Sap flow sensors

ABSTRACT

Exemplary sap flow sensors are provided. A sap flow sensor includes a substrate having a main body and at least two arms spaced apart from one another. The at least two arms extend from the main body. The sap flow sensor further includes a sap flow gauge that is disposed on the substrate. The sap flow gauge is configured to monitor a flow rate of sap through a stem of a plant. The sap flow gauge includes a heating element coupled to an arm of the at least two arms. The sap flow gauge further includes a first temperature sensor and a second temperature sensor disposed on opposite sides of the heating element. The first temperature sensor and the second temperature sensor each coupled to a neighboring arm of the at least two arms.

PRIORITY STATEMENT

The present application claims priority to U.S. Provisional PatentApplication Ser. No. 63/136,781, filed Jan. 13, 2021, which isincorporated by reference herein in its entirety.

FIELD

The present disclosure relates generally to sap flow sensors formonitoring the flow rate of sap through a portion of a plant (e.g., thestem of a plant) and, more particularly, to self-contained sap flowsensors having improved structural features that reduce sensor noise.

BACKGROUND

Sap flow measurement techniques have proven instrumental for studyingplant responses to changing environmental conditions. For example, sapis the fluid (chiefly water with dissolved sugar and mineral salts) thatcirculates the vascular system of a plant. Thus, measuring rate of whichthe sap flows through the plant can give insight into the health of theplant (or strand of a plant), the water consumption and/or usage of theplant, and/or the plant's transpiration.

Sap flow has been studied by injecting heat into the stem of plantsand/or trees. For example, a few known approaches for estimating sapflow by injecting heat include the heat pulse velocity method and theheat ratio method. Both methods utilize a sap flow gauge having aheating element and multiple temperature sensors. The heating elementcan be configured to periodically supply a fixed amount of heat to astem of the plant or tree over a period of time (typically measured inseconds), and the multiple temperature sensors measure the temperatureof the stem at two different locations. The difference in temperature atthe two locations of the stem between a certain duration after the heatpulse is fired can be used to calculate the sap flow through the stem.

However, problems exist with known sap flow gauges that utilize heatinjection for estimating sap flow. For example, many known sap flowgauges are invasive, such that they require the body of the plant to bepierced or punctured. For example, invasive sap flow gauges require botha heating probe and temperature probes to be inserted into the body ofthe plant, which results in permanent damage to the plant. In addition,invasive sap flow gauges can be difficult to install and cannot beeasily repositioned or replaced.

As such, non-invasive sap flow gauges are often favored but can be lessaccurate than the invasive alternative due to increased sensor noise.For example, a typical non-invasive sap flow gauge includes a heatingelement and temperature sensors positioned next to one another on acommon substrate. This arrangement can cause unwanted error in thetemperature measurement of the temperature sensor due to conductive heattransfer through the common substrate.

Accordingly, an improved sap flow gauge that is capable of measuring andmonitoring sap flow within one or more stems a plant, without causinginvasive damage to the plant, is desired in the art. Additionally, a sapflow gauge that advantageously minimizes sensor noise caused byconductive heat transfer through a substrate is desired.

BRIEF DESCRIPTION

Aspects and advantages of the sap flow sensors in accordance with thepresent disclosure will be set forth in part in the followingdescription, or may be obvious from the description, or may be learnedthrough practice of the technology.

In accordance with one embodiment, a sap flow sensor is provided. Thesap flow sensor includes a substrate having a main body and at least twoarms spaced apart from one another. The at least two arms extend fromthe main body. The sap flow sensor further includes a sap flow gaugethat is disposed on the substrate. The sap flow gauge is configured tomonitor a flow rate of sap through a portion of a plant. The sap flowgauge includes a heating element coupled to a first arm of the at leasttwo arms. The sap flow gauge further includes a first temperature sensorand a second temperature sensor disposed on opposite sides of theheating element. The first temperature sensor and the second temperaturesensor each coupled to a neighboring arm of the at least two arms.

In accordance with another embodiment, a sap flow sensor is provided.The sap flow sensor includes a unitary substrate composed of one or moreprinted circuit boards physically affixed to one another. The sap flowsensor further includes a sap flow gauge coupled to the one or moreprinted circuit boards. The sap flow gauge is configured to monitor aflow rate of sap through a portion of a plant by coupling to an exteriorof the portion of the plant. One or more processors coupled to the oneor more printed circuit boards and in operable communication with thesap flow gauge. The sap flow sensor further includes a memory coupled tothe one or more printed circuit boards and in operable communicationwith the one or more processors.

In accordance with another embodiment, a computing system for monitoringplants is provided. The computing system includes a plurality of sapflow sensors. Each sap flow sensor includes: a sap flow gauge, the sapflow gauge configured to monitor a flow rate of sap through a portion ofa plant by coupling to an exterior of the portion of the plant; one ormore processors in operable communication with the sap flow gauge; amemory in operable communication with the one or more processors; and anetwork interface in operable communication with the one or moreprocessors and operable to communicate using a wireless networkprotocol. The plurality of sap flow sensors are configured to operate ina mesh communications network wherein each of the sap flow sensorswirelessly communicates with at least one other of the sap flow sensorsto facilitate upload of sap flow information collected by each sap flowsensor to a central computing system.

These and other features, aspects and advantages of the present sap flowsensors will become better understood with reference to the followingdescription and appended claims. The accompanying drawings, which areincorporated in and constitute a part of this specification, illustrateembodiments of the technology and, together with the description, serveto explain the principles of the technology.

BRIEF DESCRIPTION OF THE DRAWINGS

A full and enabling disclosure of the present sap flow sensors,including the best mode of making and using the present systems andmethods, directed to one of ordinary skill in the art, is set forth inthe specification, which makes reference to the appended figures, inwhich:

FIG. 1 is a schematic illustration of a plant having multiple sap flowsensors coupled thereto, in accordance with embodiments of the presentdisclosure.

FIG. 2 illustrates an enlarged view of one of the sap flow sensors shownin FIG. 1 attached to a stem of the plant, in accordance withembodiments of the present disclosure.

FIG. 3 illustrates a sap flow sensor, in accordance with embodiments ofthe present disclosure.

FIG. 4 illustrates an alternative embodiment of the sap flow sensor, inaccordance with embodiments of the present disclosure.

FIG. 5 illustrates an alternative embodiment of the sap flow sensor, inaccordance with embodiments of the present disclosure.

FIG. 6 illustrates an alternative embodiment of the sap flow sensor, inaccordance with embodiments of the present disclosure.

DETAILED DESCRIPTION

Reference now will be made in detail to embodiments of the present sapflow sensors, one or more examples of which are illustrated in thedrawings. Each example is provided by way of explanation, rather thanlimitation of, the technology. In fact, it will be apparent to thoseskilled in the art that modifications and variations can be made in thepresent technology without departing from the scope or spirit of theclaimed technology. For instance, features illustrated or described aspart of one embodiment can be used with another embodiment to yield astill further embodiment. Thus, it is intended that the presentdisclosure covers such modifications and variations as come within thescope of the appended claims and their equivalents.

The detailed description uses numerical and letter designations to referto features in the drawings. Like or similar designations in thedrawings and description have been used to refer to like or similarparts of the invention. As used herein, the terms “first”, “second”, and“third” may be used interchangeably to distinguish one component fromanother and are not intended to signify location or importance of theindividual components.

As used herein, the terms “upstream” (or “forward”) and “downstream” (or“aft”) refer to the relative direction with respect to fluid flow in afluid pathway. For example, “upstream” refers to the direction fromwhich the fluid flows, and “downstream” refers to the direction to whichthe fluid flows. Terms of approximation, such as “generally,”“substantially,” or “about” include values within ten percent greater orless than the stated value. When used in the context of an angle ordirection, such terms include within ten degrees greater or less thanthe stated angle or direction. For example, “generally vertical”includes directions within ten degrees of vertical in any direction,e.g., clockwise or counter-clockwise.

In general, the present subject matter is directed to sap flow sensors,which include sap flow gauges configured to monitor (or measure) theflow rate of sap through a stem, branch, or other portion of a plant.Example plants on which the sap flow sensor described herein may be usedincludes, but is not limited to: corn, tomatoes, sunflower, cabbage,onion, or others. As understood by those of skill in the art, sap is thefluid, chiefly water with dissolved sugars and mineral salts, thatcirculates the vascular system of a plant. For example, the sap flowgauges described herein may advantageously measure the sap flow rate(e.g. in m/s or cm/hr) through the xylem of a plant (e.g. the vasculartissue of a plant that conducts sap upward from the roots).

In many implementations of the present design, the sap flow sensor maygive valuable insights to both the transpiration of a plant andevapotranspiration, which can be valuable when determining plant health.For example, transpiration refers to the exhalation of water vapor froma plant, and evapotranspiration is the sum of transpiration andevaporation. As is understood by those of skill in the art, bothtranspiration and evapotranspiration is generally greatest during theday (e.g. during hours of intense sun exposure). As such, the sap flowsensors described hereinbelow advantageously give insight to the amountof water usage by a given plant throughout the day. Accordingly, in oneexample application, the sap flow sensor may be used for automaticirrigation control. For example, when the sap flow sensor detects thatthe sap flow rate has dropped below a predetermined threshold for acertain time of day, the irrigation system may automatically initiateand provide additional water to the plant. In addition, the sap flowsensor(s) may be used for surveying a crop (e.g. prior to theinstallation of an irrigation system), in order to determine whichplants in the crop utilize more water throughout the day.

In another example application, the exemplary sap flow sensors describedherein may be used for properly rationing water to an entire crop. As isunderstood, minimizing water usage can favorably reduce operating costsfor farmers or may be a necessity of farming in water-constrainedregions. Accordingly, the sap flow sensors may be installed on eachplant in a crop, in order to determine exactly how much water is used byeach plant in the crop throughout the day, thereby allowing water to beproperly rationed (e.g. not used in excess) and distributed to eachplant.

In yet another example implementation, the sap flow sensors describedherein may be used for detecting plant stress (or relative health). Forexample, the sap flow rate (e.g. over a given period of time) of a givenplant may be compared against a nominal value of that same plantspecies, in order to determine the plant's health and/or relative stresslevels. These insights can be used for determining if the plant isgetting enough nutrients from the soil, enough (or too much) sunexposure, and/or adequate water throughout the day.

FIG. 1 illustrates a plant 10 having multiple sap flow sensors 100coupled thereto. In particular, each of the sap flow sensors 100 may becoupled directly to an exterior surface 12 of the plant 10. For example,each of the sap flow sensors may be coupled to the plant 10 such thatthey only contact the exterior surface of the plant 10. In exemplaryembodiments, as discussed below, each of the sap flow sensors 100 may beself-contained, singular, and cordless (e.g. a unitary, portablestructure having a singular form factor). In this way, each of sap flowsensor 100 may couple directly to the exterior of the stem of a plantand be entirely cantilevered therefrom, such that the sap flow sensor isnot tethered to other structures via any cords or wires as shown in FIG.1 . This feature may advantageously allow each of the sap flow sensors100 to be easily moved, repositioned, or replaced without any wiring.For example, the sap flow sensor may only be physically coupled to theexterior 12 of the plant 10 stem during operation, such that no cords orwires extend from the sap flow sensor 100. In some of such embodiments,all of the data collected by the sap flow gauge may be wirelesslycommunicated (e.g. via a network interface) to a controller (e.g.,implemented by a central computing system such as, for example, acloud-based or on-premises server or other computing device). In otherembodiments, the key sap flow metrics or data from the sap flow gaugemay be aggregated on the sap flow sensor 100 itself, such that not allthe data needs to be communicated.

FIG. 2 illustrates an enlarged view of a portion of the plant 10, towhich a sap flow sensor 100 is attached. In particular, FIG. 2illustrates a stem or petiole 11 of the plant 10 having a sap flowsensor 100 in accordance with the present invention attached thereto.The sap flow sensor 100 may be configured to measure the rate at which aflow of sap 14 passes through the stem 11. As shown in FIG. 2 , the sap14 generally flows from the ground, through the stems of the plant 10,to the shoots.

In particular embodiments, the sap flow sensor 100 may be composed of asubstrate 102 having a main body 18 and one or more arms 20 that extendfrom the main body 18. In many embodiments, the one or more arms 20 maycontact the exterior surface 12 of the plant 10 in operation of the sapflow sensor 100. In some embodiments, only the one or more arms 20 maycontact the exterior surface 12 of the plant 10 in operation of the sapflow sensor 100, such that the main body 18 is cantilevered from theplant 10 and extends into the ambient environment (e.g. the air oratmosphere).

In various embodiments, the arms 20 and/or the main body 18 of the sapflow sensor 100 may be rigid (e.g. inflexible), thereby advantageouslyproviding additional structural integrity and strength to the sap flowsensor 100. In such embodiments, the substrate 102 may be partially orentirely composed of a printed circuit board (PCB). For example, theprinted circuit board may include layers of copper or other conductivematerial laminated onto and/or between sheet layers of a non-conductivesubstrate. Further, in such embodiments, the temperature sensors 24, 26and/or the heating element 22 (as well as any other components) may besoldered onto the PCB to both electrically connect and mechanicallyfasten them to it. The PCBs described herein may be single-sided (onecopper layer), double-sided (two copper layers on both sides of onesubstrate layer), or multi-layer (outer and inner layers of copper,alternating with layers of substrate). Multi-layer PCBs allow for muchhigher component density, because circuit traces on the inner layerswould otherwise take up surface space between components.

In other embodiments, the arms 20 and/or the main body 18 of the sapflow sensor 100 may be malleable or flexible (e.g. compliant such thatthey can bend without breaking). In such embodiments, the arms 20 maybend or flex to correspond to the contour of the exterior surface 12 ofthe plant 10. Additionally, in such embodiments, the substrate 102 maybe composed of a flexible printed circuit board. For example, theflexible printed circuit board may be a thin insulating polymer filmhaving conductive circuit patterns affixed thereto, which, in someembodiments, may be supplied with a thin polymer coating to protect theconductor circuits. In embodiments utilizing a flexible printed circuitboard, the substrate 102 (or portions of the substrate 102) may benon-rigid or compliant such that it can bend around a stem having asmall diameter (e.g. 1 cm) without breaking.

As shown in FIG. 2 , and described in more detail below, the sap flowsensor 100 may further include a heating element 22, a first temperaturesensor 24, and a second temperature sensor 26 spaced apart from oneanother and disposed on the one or more arms 20. in the particularembodiment shown in FIG. 2 , each of the heating element 22, the firsttemperature sensor 24, and the second temperature sensor 26 may bedisposed on a respective arm 20 of the one or more arms 20 (such thatthe sensor 100 includes at least three arms in some embodiments). Inother embodiments, as will be discussed, the sap flow sensor 100 mayinclude only two arms, such that the temperature sensors 24, 26 aredisposed on one arm, and the heating element 22 is disposed on anotherarm 20. Each of the temperature sensors 24 and 26 described herein maybe any one of, but not limited to, the following: HDC2080, Thermocouple,Thermistor, RTD, or other suitable temperature measurement sensor.

In exemplary embodiments, the heating element 22, the first temperaturesensor 24, and the second temperature sensor 26 may be mutually alignedalong a common axis 30, which advantageously provides for increasedaccuracy when measuring a flow of sap 14. As shown in FIG. 2 , thecommon axis 30 may be generally parallel to both the flow of sap 14 andthe stem 11, which increases the accuracy of the sap flow measurement.

During operation of the sap flow sensor 100, the heating elementtransmits heat pulses to the stem 11 at a pre-determined frequency(which can be adjusted by a user). The temperature sensors 24 and 26 maybe spaced apart from the heating element 22 and may measure thetemperature of the stem 11 on either side of the heating element 22. Thetemperature measurements may then be analyzed using a controller inorder to determine the rate at which the flow of sap 14 is passingthrough the stem 11. In many embodiments, controller may utilize theheat ratio method (HRM) in order to calculate the heat pulse velocity(V_(h)) of the flow of sap 14. For example, in some implementations, theheat pulse velocity can be calculated according to the followingequation:

$V_{h} = {\frac{k}{x}{\ln\left( \frac{\Delta\;{tc}\; 1}{\Delta\;{tc}\; 2} \right)}}$

Where Δtc1 is the downstream temperature difference between tc1 beforethe heat pulse is fired and after the heating pulse has subsided,similarly Δtc2 is the upstream temperature difference. x is the distancebetween the heating element and temperature sensors. k is the thermaldiffusivity constant (units cm²/s), and k may be obtained by thefollowing equation:

$k = \frac{x^{2}}{4*t_{m}}$

Where t_(m) is time between heat pulse and maximum temperature riseunder zero sap flow conditions. In many implementations, the heat pulsevelocity (V_(h)) may be adjusted for the effect of non-hydroactivematerials, including the gauge and bark, to sap velocity (V_(s)), whichmay be calculated according to the following equation:V _(s) =V _(h) *m _(sap)

Where m_(sap) is the constant that offsets effects of these materials onheat transfer.

In exemplary implementations, as shown in FIG. 1 , multiple sap flowsensors 100 may be provided or installed onto a single plant 10, whichadvantageously provides spatial resolution. For example, the multiplesap flow sensors 100 may be positioned on different portions of theplant 10, in order to determine which portion of the plant is thehealthiest and/or the least healthy. In some embodiments, the multiplesap flow sensors 100 may provide spatial resolution that can be used todetect diseased portions of the plant. In another example, sap flowmeasurements retrieved from multiple portions of the plant can beaggregated to generate a single sap flow measure for the plant which hasimproved accuracy due to readings coming from multiple differentportions of the plant.

FIG. 3 illustrates a sap flow sensor 100 having a sap flow gauge 101,which is decoupled from a plant 10, in accordance with embodiments ofthe present disclosure. The sap flow sensor 100 may define alongitudinal axis L and a transverse axis T that are mutuallyperpendicular to one another. As used herein, the term “longitudinally”refers to the relative direction that is substantially parallel and/orcoaxially aligned to a longitudinal centerline 150 of the sap flowsensor 100, and the term “transversely” may refer to the relativedirection that is substantially perpendicular to the longitudinalcenterline 150 of the sap flow sensor 100.

In many embodiments, the sap flow sensor 100 may include (e.g. becomposed of) a substrate 102, and the sap flow gauge 101 may be disposedon the substrate 102. The substrate 102 may include a main body 18 andat least two arms 20, which are spaced apart from one another and eachextend from the main body 18. In particular, the arms 20 may extend fromthe main body 18 of the substrate 102 such that they are cantileveredfrom the main body. In the embodiment shown in FIG. 3 , the at least twoarms 20 may include a first arm 104, a second arm 106, and a third arm108. Each of the arms 104, 106, and 108 may extend from a respectiveconnection point 110, 112, 114, at which each respective arm 104, 106,108 is coupled to the main body, to a respective free end 116, 118, 120,at which each of the respective arms 104, 106, 108 terminates.

In particular embodiments, the first arm 104 and the third arm 108 ofthe sap flow sensor 100 may each include a diverging portion 122, aparallel portion 124, and a converging portion 126. Each divergingportion 122 may diverge away from the longitudinal centerline 150 asthey extend from the respective connection point 110 to the respectiveparallel portion 124. Each parallel portion 124 may extend generallyparallel to the longitudinal centerline 150 from the respectivediverging portion 122 to the respective converging portion 126. Eachconverging portion 126 may converge towards the longitudinal centerline150 as they extend from the respective parallel portion 124 torespective free end 116, 120.

The second arm 106 may be disposed transversely between the first arm104 and the second arm 106. In particular embodiments, the second arm106 may extend entirely along the longitudinal centerline 150 of the sapflow sensor 100 (e.g. entirely parallel to the longitudinal directionL). In many embodiments the second arm 106 may include a first portion128 that extends from the connection point 112 to a second portion 130,and the first portion 128 may define a transverse width that is lessthan the transverse width of the second portion 130.

In many embodiments, as shown, the sap flow gauge 101 may include aheating element coupled to an arm 20 of the at least two arms 20.Additionally, the sap flow gauge 101 may include a first temperaturesensor 24 and a second temperature sensor 26 disposed on opposite sidesof the heating element 22 and each coupled to a neighboring arm 20 ofthe at least two arms 20. For example, in exemplary embodiments, thefirst temperature sensor 24 may be coupled to the first arm 104, theheating element 22 may be coupled to the second arm 106, and the secondtemperature sensor 24 may be coupled to the third arm 108. In particularembodiments, as shown, the first temperature sensor 24 may be coupled tothe converging portion 126 of the first arm 104, and the secondtemperature sensor 26 may be coupled to the converging portion 126 ofthe third arm 108. Additionally, the heating element 22 may bepositioned on the second portion 130 of the second arm 106 transverselybetween, and longitudinally aligned with, the first temperature sensor24 and the second temperature sensor 26.

The spacing between the arms 104, 106, and 108 in the manner shown inFIG. 3 and described herein advantageously prevents the temperaturesensors 24, 26 from picking up thermal noise that could otherwiseconductively travel from the heating element 22 through the substrate102. For example, the heating element and the temperature sensors 24, 26being positioned on separate arms 20 and away from the main body 18 canadvantageously reduce and/or entirely eliminate sensor error (or noise)that would otherwise be caused by conductive heat transfer through thesubstrate 102. In many embodiments, the arms 104, 106, 108 maycollectively define openings 132 that advantageously reduce the areathrough which heat could travel on the substrate 102, thereby favorablyreducing sensor noise in the temperature sensors 24 and 26.

In many embodiments, as shown the first temperature sensor 24 and thesecond temperature sensor 26 are disposed equidistant from the heatingelement 22. For example, the temperature sensors 24, 26 may betransversely spaced apart from the heating element 22 by a distance 134.In some embodiments, the distance 134 may be between about 0.1centimeters and about 0.2 centimeters. In other embodiments, thedistance 134 may be between about 0.1 centimeters and about 0.1centimeters. In various embodiments, the distance 134 may be betweenabout 0.4 centimeters and about 0.8 centimeters. In particularembodiments, the distance 134 may be between about 0.5 centimeters andabout 0.7 centimeters. The distances 134 disclosed herein have beenproven to optimize sensor performance while minimizing unwanted noise.In some implementations, the first temperature sensor 24 and the secondtemperature sensor 26 may be movable relative to the heating element 22,thereby permitting a user to adjust the distance 134.

In exemplary embodiments, the converging portions 126 of both the firstarm 104 and the third arm 108 may be spaced apart from the secondportion 130 of the second arm 106 such that a gap 136 is definedtherebetween. These gaps 136 have been proven to advantageously reduceand/or entirely eliminate sensor error (or noise) that would otherwisebe caused by conductive heat transfer through the substrate 102 betweenthe heating element 22 and the temperature sensors 24, 26.

In many embodiments, the heating element 22, the first temperaturesensor 24, and the second temperature sensor 26 may each be spaced apartfrom the main body 18 by a distance 140, which, in some embodiment, maybe between about 0.1 centimeters and about 3 centimeters. In otherembodiments, the distance 140 may be between about 0.2 centimeters andabout 2 centimeters. In exemplary embodiments, the distance 140 may bebetween about 0.4 centimeters and about 0.8 centimeters. The distance140 advantageously positioned the temperature sensors 24, 26 and theheating element 22 away from the main body 18, thereby allowing the mainbody to include on board power and computing elements (which couldotherwise cause sensor error due to thermal noise).

In many embodiments, as shown, the sap flow sensor 100 may include anon-board power supply 142 physically affixed to the main body 18 of thesubstrate 102. The on-board power supply 142 may be operativelyconnected to the temperature sensors 24, 26 and the heating element 22.In some embodiments, the on-board power supply 142 can be an on-boardbattery, such as an on-board lithium-ion battery or other suitablebattery. In other embodiments, the sap flow sensor 100 may not include abattery, such that the sap flow sensors may employ one or more energyharvesting techniques. In such embodiments, the sap flow sensor 100 maybe powered by one or more solar panels. In various embodiments, the sapflow sensor 100 can also be electrically connectable (e.g., via a microUSB port or other electrical and/or data connection port) to a walloutlet or other source of utility power or other appropriately ratedpower. Plugging the sap flow sensor into a wall outlet can recharge theon-board battery.

In various implementations, as shown, the sap flow sensor 100 mayinclude one or more processors 144 and a memory 146 coupled directly tothe substrate 102 and in operable communication with the sap flow gauge101, which advantageously allows the gauge 101 to collect and store sapflow data locally on the sap flow sensor 100. The one or more processors144 and the memory 146 may be operatively connected to each of thetemperature sensors 24, 26, the heating element 22, and the power source142. The one or more processors 144 can be any suitable processingdevice (e.g., a processor core, a microprocessor, an ASIC, a FPGA, acontroller, a microcontroller, etc.) and can be one processor or aplurality of processors that are operatively connected. The memory 146can include one or more non-transitory computer-readable storage media,such as RAM, ROM, EEPROM, EPROM, one or more memory devices, flashmemory devices, etc., and combinations thereof.

The memory 146 can store information that can be accessed by the one ormore processors 144. For instance, the memory 146 (e.g., one or morenon-transitory computer-readable storage mediums, memory devices) canstore data (e.g. form the temperature sensors 24, 26) that can beobtained, received, accessed, written, manipulated, created, and/orstored. The memory 146 can also store computer-readable instructionsthat can be executed by the one or more processors 144. The instructionscan be software written in any suitable programming language or can beimplemented in hardware. Additionally, or alternatively, theinstructions can be executed in logically and/or virtually separatethreads on processor(s) 144. For example, the memory 146 can storeinstructions that when executed by the one or more processors 144 causethe one or more processors 144 to perform any of the operations and/orfunctions described herein.

The sap flow sensor 100 may further include a network interface 148coupled to the substrate 102 (e.g. coupled directly to the main body ofthe substrate). The network interface 148 can include any number ofcomponents to provide networked communications (e.g., transceivers,antennas, controllers, cards, etc.). In some implementations, thenetwork interface 148 may be operable to communicate using a wirelessprotocol, such as, for example, Wi-Fi, cellular, radio, Bluetooth and/orBluetooth Low Energy. Further, the sensor 100 can be operable tocommunicate with a central computing device 160 using the wirelessprotocol. For example the central computing device 160 can be a usercomputing device (e.g., laptop) or other computing system (e.g.,cloud-based or on-premises server system).

In some implementations, the sap flow sensor 100 communicativelyconnects to the central computing device 160 over via the networkinterface using the wireless protocol. In many implementations, thecentral computing device 160 can perform data curation and/or collectionfrom the sap flow gauge 101. In particular, in some implementations,when connected to sap flow sensor 100, the computing device 160 canselect certain data stored in the sap flow sensor 100 (e.g. in thememory 146) for transfer to the central computing device 160. Inoperation, the sap flow sensor 100 can communicatively connect toanother sap flow sensor 100 (such that the sensors 100 form a meshnetwork with one another and are capable of communicating data betweeneach other).

As one example, each sap flow sensor 100 can upload data such as sapflow readings to the central computing device 160 (e.g., wirelessly viaa mesh network). In another example, data (e.g., software or firmwareupdates) can be downloaded to each sap flow sensor 100. As one example,in some implementations, each sap flow sensor 100 can store andimplement a local on-device machine learning model. The machine learningmodel can generate inferences based on the raw sensor data collected bythe gauge. For example, the inferences can be made in real time. Theinferences can be uploaded to the central computing device 160 ratherthan the raw sensor data. Having an on-device machine learning model onthe sensor 100 can therefore provide enhanced data ownership: the ownerof the sensor 100 does not need to upload the raw data but can insteadsimply upload inferences generated from the raw data. In addition,having an on-device machine learning model on the sensor 100 can savenetwork resources as the inferences are generally smaller in data sizeversus the raw data itself. In addition, having an on-device machinelearning model on the sensor 100 can enable plant-specific orcrop-specific learning to be performed on device. For example, one ormore learning routines or algorithms can be performed over time as datais collected so that the on-device machine learning model is re-trainedwith the collected data to thereafter provide inferences which are moreaccurate and attuned to the particular dynamics of the plant or crop forwhich the sensors 100 are being deployed. In one example, updates to theon-device machine learning model can be downloaded to each sensor 100(e.g., wirelessly via a mesh network) and applied to update the localmodel at the sensor 100. In some implementations, parameters such asheat duration (i.e. the duration of a heat pulse applied to the plant bythe heating element) and/or heat ratio window may be machined learnedvia the machine learning model described herein, which may beadvantageous because such parameters are likely to vary between plantspecies.

Directly coupling the computing components (e.g. 142, 144, 146, and 148)to the substrate 102 of the sap flow sensor 100 advantageously allowsthe sap flow sensor 100 to be self-contained, singular, portable, andcordless. Additionally or alternatively, one or more of the computingcomponents (e.g. 142, 144, 146, and 148) may be disposed on a separatePCB, which may be electrically and physically coupled directly to themain body 18 via a pin bank 162 (thereby allowing the sap flow sensor100 to remain cordless in such embodiments). Each of sap flow sensor 100may couple directly to the exterior of the stem of a plant 10 and beentirely cantilevered therefrom, such that the sap flow sensor 100 isnot tethered via any cords or wires as shown in FIG. 1 . This featuremay favorably allow each of the sap flow sensors 100 to be easily moved,repositioned, or replaced without any wiring. In such embodiments, allof the data collected by the sap flow gauge may be wirelesslycommunicated (e.g. via a network interface) to a central computingdevice 160.

FIG. 4 illustrates a sap flow sensor 200 having a sap flow gauge 201,which is decoupled from a plant 10, in accordance with an alternativeembodiment of the present disclosure. The sap flow sensor 200 may definea longitudinal axis L and a transverse axis T that are mutuallyperpendicular to one another. As used herein, the term “longitudinally”refers to the relative direction that is substantially parallel and/orcoaxially aligned to a longitudinal centerline 250 of the sap flowsensor 200, and the term “transversely” may refer to the relativedirection that is substantially perpendicular to the longitudinalcenterline 250 of the sap flow sensor 200.

In many embodiments, the sap flow sensor 200 may include (e.g. becomposed of) a substrate 202, and the sap flow gauge 201 may be disposedon the substrate 202. The substrate 202 may include a main body 18 andat least two arms 20, which are spaced apart (e.g. transversely) fromone another and each extend from the main body 18. In particular, thearms 20 may extend from the main body 18 of the substrate 202 such thatthey are cantilevered from the main body 18. In the embodiment shown inFIG. 4 , the at least two arms 20 may include a first arm 204 and asecond arm 206. The first arm 204 and the second arm 206 may extend froma respective connection point 208, 210, at which each respective arm204, 206 is coupled to the main body 18, to a respective free end 212,214, at which each of the respective arms 204, 206 terminates. Inparticular embodiments, the first arm 204 may define a notch 215 in thetransverse direction T, and the second arm may include a transverseportion 216 that extends into the notch 215 but does not contact thefirst arm 204. In some embodiments, the second arm 206 may extendentirely along the longitudinal centerline 250 of the sap flow sensor200 (e.g. entirely parallel to the longitudinal direction L).

In many embodiments, as shown, the sap flow sensor 200 may furtherinclude a sap flow gauge 201 having a heating element coupled to an arm20 of the at least two arms 20. Additionally, the sap flow gauge 201 mayinclude a first temperature sensor 24 and a second temperature sensor 26disposed on opposite sides of the heating element 22 and each coupled toa neighboring arm 20 of the at least two arms 20. For example, inexemplary embodiments, the first temperature sensor 24 and the secondtemperature sensor may be coupled to the first arm 204 on opposite sides(e.g. opposite longitudinal sides) of the heating element 22. Theheating element 22 may be coupled to the second arm 206, particularlycoupled to the transverse portion 216 of the second arm 206 between thetemperature sensors 24 and 26.

The spacing between the arms 204, 206 in the manner shown in FIG. 4 anddescribed herein advantageously prevents the temperature sensors 24, 26from picking up thermal noise that could otherwise conductively travelfrom the heating element 22 through the substrate 202 to the temperaturesensor 24 or 26. For example, the heating element 22 and the temperaturesensors 24, 26 being positioned on separate arms 20 and away from themain body 18 advantageously reduces and/or entirely eliminates sensorerror (or noise) that would otherwise be caused by conductive heattransfer through the substrate 102.

In many embodiments, as shown the first temperature sensor 24 and thesecond temperature sensor 26 are disposed equidistant from the heatingelement 22. For example, the temperature sensors 24, 26 may belongitudinally spaced apart from the heating element 22 by a distance234. In some embodiments, the distance 234 may be between about 0.1centimeters and about 0.2 centimeters. In other embodiments, thedistance 234 may be between about 0.1 centimeters and about 0.1centimeters. In various embodiments, the distance 234 may be betweenabout 0.4 centimeters and about 0.8 centimeters. In particularembodiments, the distance 234 may be between about 0.5 centimeters andabout 0.7 centimeters. The distances 234 disclosed herein have beenproven to optimize sensor performance while minimizing unwanted noise.

In many embodiments, the heating element 22, the first temperaturesensor 24, and the second temperature sensor 26 may each be spaced apartfrom the main body 18 by at least a distance 240. For example, the firsttemperature sensor 26 may be spaced apart by exactly the distance 240,and the heating element 22 and the second temperature sensor are spacedapart a greater distance. In some embodiments, the distance 240 may bebetween about 0.1 centimeters and about 3 centimeters. In otherembodiments, the distance 240 may be between about 0.5 centimeters andabout 2 centimeters. The distance 240 advantageously positioned thetemperature sensors 24, 26 and the heating element 22 away from the mainbody 18, thereby allowing the main body 18 to include on board power andcomputing elements (which could otherwise cause sensor error due tothermal noise).

FIG. 5 illustrates a sap flow sensor 300 having a sap flow gauge 301that is offset from the main body 18 in the transverse direction T, inaccordance with an alternative embodiment of the present disclosure. Thesap flow sensor 300 may define a longitudinal axis L and a transverseaxis T that are mutually perpendicular to one another. As used herein,the term “longitudinally” refers to the relative direction that issubstantially parallel and/or coaxially aligned to a longitudinalcenterline 350 of the sap flow sensor 300, and the term “transversely”may refer to the relative direction that is substantially perpendicularto the longitudinal centerline 350 of the sap flow sensor 300.

As shown, the sap flow sensor 300 may include a tab 302 extendingtransversely from the main body 202. This may advantageously increasethe distance between the components disposed on the at least two arms 20(e.g., the heating element 22 and the temperature sensors 24 and 26) andthe components on the main body 18 (e.g., the power supply 142, theprocessors 144, memory 146, the network interface 148, and othercomponents disposed on the main body 18). For example, the main body 18may be shaped generally rectangularly, and the tab 302 may extendtransversely from one of the corners of the main body 18. As shown inFIG. 5 , the at least two arms 20 may extend directly from the tab 302.In particular, the arms 20 may extend generally longitudinally from thetab 302 such that they are cantilevered from the tab 302. The first arm204 and the second arm 206 may extend (e.g., longitudinally) from arespective connection point 308, 310, at which each respective arm 204,206 is coupled to the tab 302, to a respective free end 312, 314, atwhich each of the respective arms 204, 206 terminates. In this way, thearms 204, 206 may be offset from the main body 18 (and the longitudinalcenterline 350) in the transverse direction T. Offsetting the at leasttwo arms 20 in this manner has been proven to reduce sensor noise thatcould otherwise be caused by conductive heat transfer through thesubstrate 202.

In many embodiments, as shown, the sap flow sensor 300 may furtherinclude a sap flow gauge 301 having a heating element 22 and a pluralityof temperature sensors 311. The plurality of temperature sensors 311 maybe coupled to the first arm 204, and the heating element 22 may becoupled to the second arm 206. The heating element 22 and the pluralityof temperature sensors 311 may be aligned with one another and disposedon a common longitudinal line 318 (which is transversely offset from thelongitudinal centerline 350). In exemplary embodiments, the plurality oftemperature sensors 311 may include a first pair of temperature sensors320, a second pair of temperature sensors 322, and a third pair oftemperature sensors 324. The processors 144 may selectively collect data(which may be stored in the memory 146) from one or more of the firstpair of temperature sensors 320, the second pair of temperature sensors322, and/or the third pair of temperature sensors 324.

As shown in FIG. 5 , each temperature sensor in the first pair oftemperature sensors 320 may be spaced apart from the heating element 22by a first distance 321. Each temperature sensor in the second pair oftemperature sensors 322 may be spaced apart from the heating element 22by a second distance 323. Each temperature sensor in the third pair oftemperature sensors 324 may be spaced apart from the heating element 22by a third distance 325. The third distance 325 may be longer than thefirst distance 321 and the second distance 323. The second distance 323may be longer than the first distance 321 and shorter than the thirddistance 325. The first distance 321 may be shorter than the seconddistance 323 and the third distance 325.

Including multiple pairs of variably spaced temperature sensorsadvantageously increases the modularity of the sap flow gauge 301. Forexample, the processor 144 may selectively collect data from one of thepairs of temperature sensors 320, 322, and/or 324 depending on thebranch size, plant species, or other factors.

FIG. 6 illustrates a sap flow sensor 400 having a sap flow gauge 201, inaccordance with an alternative embodiment of the present disclosure. Asshown, the sap flow sensor 400 may be a part of an “octopus” design,such that the sap flow sensor 400 is supported by a central sap flowsensor or unit (such as any one of the sap flow sensors 100, 200, or 300described above with reference to FIGS. 3 through 5 ). In this way, thesap flow sensor 400 may not include an on-board processor, memory, orpower supply. Instead, the sap flow sensor 400 may only include anetwork interface 402 coupled to the substrate 202 (e.g. coupleddirectly to the main body 18 of the substrate). The network interface402 may be in operable communication with the network interface of acentral unit or sap flow sensor (such as the network interface 148 ofthe sap flow sensors 100, 200, or 300 described above with reference toFIGS. 3 through 5 ).

The network interface 402 can include any number of components toprovide networked communications (e.g., transceivers, antennas,controllers, cards, etc.). In some implementations, the networkinterface 402 may be operable to communicate using a wireless protocol,such as, for example, Wi-Fi, cellular, radio, Bluetooth and/or BluetoothLow Energy. In some embodiments, the network interface 402, and/or thesap flow gauge 201, may be powered by an internal battery of the networkinterface 402. In some embodiments, as shown in FIG. 6 , the sap flowsensor 400 may include one or more additional sensors 404. The one ormore additional sensors 404 may be disposed on one or both of the mainbody 202 or an arm of the at least two arms 20. In various embodiments,the one or more additional sensors 404 may be a micro-electro-mechanicalsystem (or MEMS sensor), an accelerometer, a magnetometer, and/or agyroscope. In this way, the one or more additional sensors 404 maycollect data indicative of a branch movement, wind speed, winddirection, and/or sensor orientation.

The sap flow sensors 200, 300, and 400 having only two arms 204, 206 asshown in FIGS. 4 through 6 may provide numerous advantages over sap flowsensors having more than two arms (such as three or more arms). Forexample, the sap flow sensors 200, 300, and 400 having only two arms204, 206 may better secure to the branch or stem, may produce lessrotational torque once secured, and may have reduced manufacturing costsrelative to sap flow sensors having three or more arms.

In some example embodiments, an “octopus” configuration can include aplurality of sap flow sensors (e.g., the sap flow sensor 400 of FIG. 6 )which are connected to a single central computing unit. For example,this configuration may allow a number of sap flow sensors to bepositioned at various locations on a plant (e.g., see the multiplesensor positioned at various locations on a tree as shown in FIG. 1 ),while all connecting to a single central unit. Additionally oralternatively, this configuration may allow for a number of sap flowsensors to be positioned on multiple plants in a subsection of a plot,e.g., a group of citrus trees or corn plants in a plot. The sensors canbe connected to the central unit in a wired or wireless fashion. In someexample embodiments, a majority (e.g., all) of the computationalcomponents such as processors, memory, etc. can be contained in thecentral unit. This arrangement can enable the sap flow sensors toinclude fewer computational components (e.g., as described with respectto FIG. 6 ) and therefore to be relatively lighter in weight andtherefore easier to attach to a plant.

The “octopus” configuration can also enable the central unit to receiveand process and therefore gain/produce insights and intelligence frommultiple sap flow sensors. As one example, the central unit can performanomaly or error detection for the multiple sap flow sensors. Forexample, if readings from one sap flow sensor diverge significantly fromreadings from other sap flow sensors (e.g., other sap flow sensors atrelatively similar locations) then the central unit can detect (e.g.,and transmit or surface an alert) that an error or anomaly is occurringat the sensor.

In another example, the central unit can perform sensor fusion or othersensor processing techniques on sensor data (e.g., sap flow readingsand/or accelerometer or other data) from the sensor(s). For example, amachine learning model or other algorithm can be trained and/or used tocorrect or refine sap flow sensor readings based on other sensor data(e.g., temperature data, accelerometer data, etc.). In another example,readings from a first sensor can be used to refine or correct readingsfrom one or more second, different sensors. For example, a machinelearning model or other algorithm can be trained and/or used to corrector refine sap flow sensor readings from the first sensor based on thedata from the one or more second, different sensors.

In another example, readings from multiple sap flow sensors can providea holistic view of the plant, which may enable the computing system todetermine which part of the plant (or tree) is transpiring, stressed,and/or what type of ambient conditions it is experiencing. This alsosupports and/or provides data to validate when unusual sap flow data isrecorded. For example, if a first sensor in the multiple sensors detectsan unusual sap flow, then the other sensors in the multiple sap flowsensors may be used to contextualize, verify, and/or support the unusualsap flow data. This may be done to support temporal and spatialresolution of sap flow readings. For example, if plant performance datais desired at a specific time (or time period), then the sap flowsensors may each generate heat pulses and collect sap flow dataseparately in the minutes leading up to the specified time (e.g., the 15minutes leading up). This sap flow data may be indicative of shade side(e.g., the orientation of the branch facing away from the sun), sun side(opposite the shade side), apex, under the stem for the specified time(or time period). This data may be integrated for the specified time,such that any subsequent data measured at a similar time may be comparedto the historical data.

In another example, the central unit can enable power consumptionsavings by managing or controlling operations (e.g., operations thatconsume power such as activation of the heating element) of the multiplesensors in an intelligent fashion. As one example, the central unit cansequentially power on/off the sap flow sensors to obtain respective sapflow readings. By sequentially powering on/off the sap flow sensors tocollect readings (e.g., as opposed to constantly powering the sensorsand/or powering the sensors all at once) the total amount of powerconsumed can be reduced and/or the peak power consumed can be reduced,which may be beneficial when a power supply to the sensors is limited intotal capacity and/or peak capacity (power output).

This written description uses examples to disclose the invention,including the best mode, and also to enable any person skilled in theart to practice the invention, including making and using any devices orsystems and performing any incorporated methods. The patentable scope ofthe invention is defined by the claims, and may include other examplesthat occur to those skilled in the art. Such other examples are intendedto be within the scope of the claims if they include structural elementsthat do not differ from the literal language of the claims, or if theyinclude equivalent structural elements with insubstantial differencesfrom the literal language of the claims.

What is claimed is:
 1. A sap flow sensor comprising: a substrate havinga main body, a first arm extending from the main body, and a second armextending from the main body and spaced apart from the first arm suchthat a gap is defined between the first arm and the second arm, whereinthe first arm defines a notch, and wherein the second arm includes atransverse portion extending into the notch; a sap flow gauge disposedon the substrate, the sap flow gauge configured to monitor a flow rateof sap through a portion of a plant, the sap flow gauge comprising: aheating element coupled to the transverse portion of the second arm; anda first temperature sensor and a second temperature sensor disposed onopposite sides of the heating element and each coupled to the first arm.2. The sap flow sensor as in claim 1, wherein the substrate is composedof one or more printed circuit boards.
 3. The sap flow sensor as inclaim 1, wherein the entire substrate is rigid.
 4. The sap flow sensoras in claim 1, wherein the substrate is flexible.
 5. The sap flow sensoras in claim 1, wherein the heating element, the first temperaturesensor, and the second temperature sensor are mutually aligned along acommon axis, the common axis extending across the gap.
 6. The sap flowsensor as in claim 1, wherein the first temperature sensor and thesecond temperature sensor are disposed equidistant from the heatingelement.
 7. The sap flow sensor as in claim 1, wherein the heatingelement, the first temperature sensor, and the second temperature sensorare each spaced apart from the main body by at least a distance ofbetween about 0.1 centimeters and about 3 centimeters.
 8. The sap flowsensor as in claim 1, wherein the sap flow gauge further comprises athird temperature sensor and a fourth temperature sensor disposed on thefirst arm on opposite sides of the heating element, wherein the firsttemperature sensor and the second temperature sensor are spaced apartfrom the heating element by a first distance, wherein the thirdtemperature sensor and the fourth temperature sensor are spaced apartfrom the heating element by a second distance, and wherein the seconddistance is longer than the first distance.
 9. The sap flow sensor as inclaim 1, wherein a tab extends from a corner of the main body, andwherein the first arm and the second arm extend from the tab such thatthe first arm and the second arm are offset from a centerline of themain body of the substrate.
 10. A sap flow sensor comprising: a unitarysubstrate composed of a printed circuit board, the unitary substratehaving a main body, a first arm extending from the main body, and asecond arm extending from the main body and spaced apart from the firstarm such that a gap is defined between the first arm and the second arm,wherein the first arm defines a notch, and wherein the second armincludes a transverse portion extending into the notch; a sap flow gaugecoupled to the printed circuit board, the sap flow gauge configured tomonitor a flow rate of sap through a portion of a plant by coupling toan exterior of the portion of the plant, the sap flow gauge comprising aheating element coupled to the transverse portion of the second arm, thesap flow gauge further comprising a first temperature sensor and asecond temperature sensor disposed on opposite sides of the heatingelement and each coupled to the first arm; one or more processorsdirectly coupled to the printed circuit board and in operablecommunication with the sap flow gauge; and a memory directly coupled tothe printed circuit board and in operable communication with the one ormore processors.
 11. The sap flow sensor as in claim 10, wherein the sapflow sensor is wireless.
 12. The sap flow sensor as in claim 10, whereinthe sap flow sensor further comprises a network interface coupled to theprinted circuit board and operable to communicate using a wirelessnetwork protocol.
 13. The sap flow sensor as in claim 12, wherein thewireless network protocol comprises one of radio-based communication,Wi-Fi, Bluetooth, or cellular.
 14. The sap flow sensor as in claim 10,further comprising: a real time clock coupled to the printed circuitboard and in operable communication with the one or more processors. 15.The sap flow sensor as in claim 10, wherein the first arm and the secondarm each extend from a respective connection point at the main body to arespective free end.
 16. The sap flow gauge as in claim 10, wherein theheating element, the first temperature sensor, and the secondtemperature sensor are mutually aligned along a common axis, wherein thecommon axis does not intersect the main body.
 17. A computing system formonitoring plants, the computing system comprising: a plurality of sapflow sensors, wherein each sap flow sensor comprises: a substrate havinga main body, a first arm extending from the main body, and a second armextending from the main body and spaced apart from the first arm suchthat a gap is defined between the first arm and the second arm, whereinthe first arm defines a notch, and wherein the second arm includes atransverse portion extending into the notch; a sap flow gauge, the sapflow gauge configured to monitor a flow rate of sap through a portion ofa plant by coupling to an exterior of the portion of the plant, the sapflow gauge comprising a heating element coupled to the transverseportion of the second arm, the sap flow gauge further comprising a firsttemperature sensor and a second temperature sensor disposed on oppositesides of the heating element and each coupled to the first arm; and anetwork interface in operable communication with one or more processorsand operable to communicate using a network protocol; and wherein theplurality of sap flow sensors are configured to communicate sap flowinformation to a central unit or at least one other of the sap flowsensors, and wherein each sap flow sensor is configured to store andimplement a local on-device machine learning model, the machine learningmodel configured to generate inferences based on the sap flow data andupload the inferences to the central unit or one or more sap flowsensors of the plurality of sap flow sensors.
 18. The computing systemof claim 17, wherein the plurality of sap flow sensors are configured tooperate in a mesh communications network wherein each of the sap flowsensors wirelessly communications with at least one other of the sapflow sensors to facilitate upload of the sap flow information collectedby each sap flow sensor to a central computing system.